The overall hypothesis of this application is that graft arteriosclerosis (GA), the major cause of late cardiac allograft failure, results from a chronic hot T cell response to allogeneic graft endothelial cells (ECs) that takes the form of delayed-type hypersensitivity DTH within the vessel wall, locally generating IFN-? which is responsible for driving vascular smooth muscle cell (VSMC) proliferation and intimal hyperplasia. The clinical correlations and evidence from other experimental systems have suggested that non-immune factors, especially peri-operative stress-induced alterations in the graft, are important contributors to GA pathogenesis. It is proposed and demonstrated experimentally that signals in the graft, primarily from ECs, generated as a result of peri-operative stress can produce mediators that influence T cell activation and differentiation. However, how the peri-operative stresses such as hypoxia couple intracellular signaling pathway to alter ECs alloimmunity and GA is not understood, and is the subject of this project. We have identified two major intracellular signaling proteins- cytosolic ASK1-interacting protein-1 (AIP1) and mitochondrial thioredoxin-2 (Trx2) in ECs that protect ECs from oxidative stress-induced injuries. Specifically, AIP1 in the cytoplasm via its inhibitory effect on the NADPH oxidase (Nox) while Trx2 in mitochondria via its anti-oxidant activity, prevent ischemia-reperfusion-elicited ROS and oxidative stress-induced inflammatory responses. In this proposal, we hypothesize that the responses to non-immune peri-operative injuries of graft endothelial cells (EC) are modulated by Trx2 in the mitochondria and AIP1 in the cytosol, altering the EC in a manner that affects T cell- mediated alloimmunity and GA. We propose to explore this hypothesis in the following specific aims: 1) Characterize AIP1-regulated cytosolic signaling pathways that mediate peri-operative stress-induced responses that alter EC immunogenicity and GA progression. 2) Characterize Trx2-regulated mitochondrial signaling pathways that mediate peri-operative stress-induced responses that alter EC immunogenicity and GA progression. If successful, this study will provide therapeutic strategies by modulating these two molecules in ECs to reduce GA incidence or delay GA progression.